I've sponsored people for several events and it always has been extremely straightforward and super easy. I've always registered for the event for myself, as though I was going. This means that I put the event ticket on my credit card, retained full control of the RSP, and when it came time for Disney to charge the RSP items, they charged my card.
However, in order to switch the registration from my name to my sponsor's name (and I'm very well-aware of Disney's policy of checking in event guests), I simply called event services and requested a proxy form. I think there's even an established time frame in which to transfer ticket names from one guest to another. It has been a few years, but I think I might have filled it out and faxed it back and the registration was switched from my name to my sponsor - however the payment arrangements remained established on my credit card.
I hope this helps. If you have any problems, call event services. I've always found them extremely helpful in sorting out problems like this.